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The Purpose DNA has to replicate in order to produce identical genetic material that is distributed equally when cells divide. Therefore almost all cells in the human body should contain identical DNA. DNA replication is semiconservative, meaning that each product of replication, or daughter strand, is composed of one strand from the parent DNA molecule and one newly synthesized strand. The Process 1. DNA gyrase relieves tension in the DNA strands created by the unwinding 2. DNA helicase disrupts the hydrogen bonds that anneals nitrogenous bases to unzip the double helix 3. Single-stranded binding proteins bind to the exposed DNA strands to prevent re-annealing 4. Primase creates RNA primers that attach to the DNA strand where replication is to begin 5. DNA polymerase III begins at the primers and synthesizes complementary strands using the original strand as a template 6. DNA polymerase I replaces the RNA fragments with DNA fragments that are complementary to the template strand in that section 7. DNA ligase closes the remaining gaps in DNA by catalyzing bonds on the sugar-phosphate backbone 8. DNA polymerase I and III check for errors in the base pairing and corrects them The Direction DNA replication begins in a number of spots along DNA strands and continues in either direction from this point. This forms replication bubbles. DNA template strands are read in the 3' to 5' direction and complementary strands are therefore synthesized in the 5' to 3' direction. The leading strand is the new strand that is synthesized continuously in this direction, towards the replication fork. The lagging strand is the new strand that is synthesized discontinously away from the replication fork. The short fragments created by the discontinuous pattern are called Okazaki fragments. After all gaps are filled in and errors are edited, two identical daughter DNA molecules are left. |
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Addressing Misconceptions
- "DNA replicates in the 5' to 3' direction" means DNA polymerase moves along the template strand from the 5' end to the 3' end.
- DNA replication occurs beginning at one end of a strand towards the other